OK.
Let me put it in an other way. Maybe I am wrong since I don't have the time to open any textbooks.
Step by step:
#1. CO2 in water.
CO2 + H20 <-----> HCO3- and (H+) <-------> CO3-- and (H+)
#2. NaOH in water.
NaOH + H20 ------> Na+ and (OH-) (NaOH Maintains a relatively constant alkalic pH throughout the life of the scrubber)
#3 Ca(OH)2 in water
Ca(OH)2 <-------> Ca++ and 2(OH-) This is a weak base but provides a source of Ca++ as well as OH-
The neutralisation of CO2 is taking place in an aquatic solution where the following reaction is taking place:
#4 Neutralisation of CO2 and formation of CaCO3
(H+) from CO2 solution reacts with (OH-) from the base system in the scrubber.
H+ and OH- gives H2O
Ca++ and CO3-- gives CaCO3. Therefore more and more HCO3- is sifted to the right and form CO3-- untill all CO2 is being neutralised. See Note below why this reaction is shifted to right:
NOTE: It is a common principle that when there is a removal of the products by means of volatile gases or insoluble substances (CaCO3) the reaction is shifted towards the side of the products. Therefore the neutralisation of CO2 is complete as long as there is a source of OH-.
END OF SCRUBBER LIFE:
The source of OH- has been exhausted. A little more CO2 in the system and there is no more capacity to neutralise it. CO2 as it disolves in the water gives an excess of H+. There is a lot CaCO3 formed, still an aquatic solution of Na+ some Ca++ maybe an excess of H+ some HCO3-. NaOH is never reformed from the time it disolves in the water solution. It is present in the form of Na+ and OH- untill the capacity of the particular pellet to neutralise CO2 is full.
NOTE2: The scrubber It is not an homogenous solution. There is a formation of a solution on the surface of the pellets where all the reactions are taking place.
CHANGE OF COLOR.
There is a dye inside the pellets. This dye has a form of
AH <---------------> A- and H+
This dye may exist in two forms AH which is the acid form and A- which is the alkali form. The concentration of H+ determines which form predominates. It happens that AH form has a different color than A- . AH is pink! To see that take some used pink scrubber and pure some caustic soda on it. You will see the pink disappearing.
Whereever there is change of color the system of alkalis may no longer provide OH- to neutralise CO2, hence the CO2 moves to the next layer where it reacts.
Na2CO3 actually does not exist in aquatic solutions. Sodium ions are always present and their source is NaOH.
Are there any chemists to evaluate this approach? Any critisism welcome!
